More specifically, the present invention relates to a unit of the type comprising a conveyor belt extending along a given path; feed means located along said path to feed a continuous mat of shredded tobacco onto said conveyor belt; and suction means located on the opposite side of said conveyor belt to said feed means, and cooperating with said feed means to retain said continuous mat of shredded tobacco on said conveyor belt.
In cigarette manufacturing, the continuous mat is fed onto a continuous strip of paper, which is folded transversely about the mat to form a continuous cigarette rod, which is then cut into cigarette portions, which in turn are subsequently cut and rolled to form a succession of normally filter-tipped cigarettes.
When cutting and rolling the cigarette portions, the tobacco particles inside tend to separate and spill from the ends of the cigarette portions. To eliminate this drawback, the continuous cigarette rod is so formed that, when cut into cigarette portions, the density of the tobacco at the ends of the cigarette portions is greater than that of the tobacco in the intermediate portions of the cigarette portions.
This is normally achieved, in units for forming a continuous mat of tobacco of the type described above, using pressure devices located downstream from the feed means to compact given portions of the continuous mat of tobacco, or using shaving disks, also located downstream from the feed means and having peripheral cavities arranged so that the mat of tobacco is shaved less or not at all at given areas spaced along the mat of tobacco with a spacing equal to the length of the cigarette portions to be produced.
Though widely used, the above methods do not always succeed in achieving the desired result, owing to the mat of tobacco simply comprising a totally heterogeneous bed of shredded dry leaves, whose response to external processing differs from one point to another.
To eliminate this drawback, as opposed to variously processing the mat of tobacco, it has been proposed to obtain denser portions along the mat by adding to the mat a succession of localized masses of tobacco. In U.S. Pat. Nos. 3,795,249 and 4,693,262, for example, denser portions are achieved by depositing on the conveyor belt, upstream from the feed means, extra amounts of tobacco, which are fed beforehand by further feed means to respective suction radial seats on a wheel external to the conveyor belt and positioned with a lateral surface tangent to the conveyor belt. By virtue of said suction means, the extra quantities of tobacco are deposited on the conveyor belt at the point of tangency between the wheel and the conveyor belt.
This solution obviously has major drawbacks, owing to the wheel being located outside the tobacco feed means. That is, transferring the masses of tobacco formed on the wheel to the conveyor belt seriously complicates the structure of the unit, and involves repeated handling of the shredded tobacco, thus reducing the quality of the finished cigarettes.